I tested using steel drill bits as projectiles out of my smoothbore .177 coaxial gun, and the grooves in the bit acted as rifling and enabled the bit to fly straight and penetrate deeply without fins. I don't have the means to test this out from far away, or at stronger targets such as steel sheets so if anyone wants to try it.(JSR? )

It doesn't sound like it's self-stabilising then, at least not efficiently enough to be worth the high cost of drill bits. I wouldn't be surprised to have similar proportions of unstabilised projectiles not yet tumbling at those distances.